The present invention concerns a crosslapper for transforming a web into a fleece by folding.
Such machines are known, in which a web of fibres, coming for example from a card, is first of all transported by a first conveyor belt, called a front conveyor belt, to a pinching zone where it is held between the conveyor belt and a second conveyor beltxe2x80x94or rear conveyor beltxe2x80x94which transport it to a lapping carriage.
The lapping carriage has a lapping slot facing downwards, through which the web is released whilst the lapping carriage reciprocates above an output apron. The web is thus accordion folded on the output apron. At the same time, the output apron moves substantially perpendicularly to the direction in which the front and back conveyor belts are moving. Thus, instead of being exactly piled on one another, the successive segments of web between two folds are offset in a zigzag pattern along the output apron. The continuous fleece thus formed is to undergo a bonding and/or compaction treatment, consisting for example in needling.
The transport path of the web in the crosslapper also passes through a reciprocable storage carriage to regulate the length of the path between the entry zone of the web into the crosslapper and the lapping slot, and thus regulate the speed at which the web is fed through the lapping slot.
The web, essentially made up of longitudinal fibers that are very loosely connected and together form a highly aerated structure, has a very low mechanical strength. However, it is necessary that during passage through the crosslapper, the web maintains its initial dimensions as much as possible, that is in particular its initial width and the uniform distribution of its weight over the width. However, manipulations undergone by the web in the crosslapper endanger this desired stability.
In the past, many machines were used to try to remedy this difficulty by increasing the length of the pinching zone. This often led to the creation of an additional turn in the path of the web in the middle of the pinching zone, see in particular FR-B-2 553 102, or even to placing the storage carriage in the middle of the pinching zone, see in particular FR-A-2 234 395. This was intended to remedy defects found on even older machines such as those described according to U.S. Pat. No. 1,886,919 where 180xc2x0 turns of the web were carried out whilst the web was exposed on the outside of the turn, with many disadvantages related to the centrifugal force and major differences in performance according to the direction of movement of the carriage where the turn was made.
By comparison with this old prior art (U.S. Pat. No. 1,886,919; FRB 2 234 395, FR-B-2 553 102), EP-A-0 517 563 made possible a spectacular increase in speeds of industrial treatment of the web by showing how to combine a substantially rectilinear pinching zone extending from one carriage to the other, with exposed transportation upstream from the storage carriage, and a two-part turn in the storage carriage including a first turn making the web pass from a horizontal path to a sloping path, then a second turn at an angle greater than 90xc2x0 and less than 180xc2x0 with a first pinching line for the web between the two conveyor belts in an intermediate angular position of this second turn.
This structure made it possible to almost double the industrial travelling speed of the web in the crosslapper, which thus increased from approximately 80 m/min to approx. 150 m/min.
A phenomenon observed according to the invention when it was attempted to exceed this speed with a structure according to EP-A-0 517 563 is that the pinching line located in an intermediate position on the second partial turn of the storage carriage tends to expell the air from the web in an upstream direction. The result is a swelling and deformation of the web upstream of the pinching line, then a radial expansion of the web when the web passes through the pinching line.
WO-A-97/19 209 shows how to create a first pinching zone with a slightly convergent shape along the oblique descending part between the two partial turns in the storage carriage, then to arrange several pinching lines along the whole of the second partial turn, with a first pinching line just upstream and a last pinching line just downstream of the turn.
In practice, this complex solution does not bring any improvement since it multiplies the compression-decompression cycles to which the web is subjected in the turn.
Moreover, it has also been found according to the invention that the search for increased speeds was also tending to lead to a problem of web deformation in the. lapping carriage during recompression of the web in the lapping slot. WO-A-97/19 209 does not propose any solution applicable to the lapping carriage.
The object of the invention is thus to propose a crossslapper for guiding the web through at least one turn, made up of a structure allowing to increase the travelling speed of the web in the crosslapper without leading to unacceptable deformation of the web.
According to the invention, the crosslapper including:
at least two endless conveyor belts that together define, for a fibre web, a transport path extending from an entry zone to a lapping slot;
at least one lapping carriage having guiding rollers for the two conveyor belts and on which the lapping slot is formed;
an output apron which is movable under the lapping slot substantially parallel to the axes of the guide rollers,
the path forming at least one turn against the outer surface of one of the conveyor belts in a zone where the inner surface of this conveyor belt rests on an internal guide roller, the web being exposed on an initial angular area of the turn, then being restricted radially outwards by a support zone belonging to the other conveyor belt within a second, angular area of the turn,
is characterised in that the support zone is guided according to a curvature ranging from convex with a radius greater than the inner guide roller, to concave substantially following the outer circumference of the web.
According to the invention it was found that is was advantageous:
on one hand to keep the exposed condition along a beginning of the turn, in said first angular area, along which the web is more or less supported by its own weight and by a certain tendency to adhere to the internal conveyor belt; and
on the other hand to transform the pinching line of the prior art into a distributed support structure that may consist of a flat section of the external conveyor belt, of a section of the external conveyor belt supported by a large diameter external roller, or even by a simulated section with inverted curvature, hence concave on the web side, by means of a succession of at least two external rollers along the second angular area of the turn.
In the storage carriage, the version where the support zone comprises a flat section of the external conveyor belt has turned out to be especially advantageous. Such a support structure behaves like an active deflector, which drives the web into the second part of the turn around the internal roller, in a continuous way over quite a large second angular area. By comparison with the pinching line of EP-A-0 517 563, the flat section channels and propels the web into its turn much earlier, whilst supporting it further downstream towards the longitudinal section of the pinching zone. In this respect, it is particularly advantageous for the external surface of the flat section, which is the one that is active in terms of textiles, to face obliquely upwards.
It is also advantageous in the storage carriage that the web is free of any support upstream of the second angular area and in particular along the downwardly sloping section between the two partial turns.
It is also advantageous, in the storage carriage, that downstream of the second angular area, the web runs through a third angular area free of external support until the web is supported by the longitudinal section of the external conveyor belt extending into the pinching zone. The longitudinal section of the external conveyor belt is preferably supported by a roller placed a little behind the internal roller in relation to the direction of movement of the web, so as not to form a rigid pinching line at the turn exit, contrary to what is recommended by WO-97/19209.
According to another feature of the invention with its own specific interest, the pinching zone extends in a rectilinear direction in a slightly descending slope from the storage carriage to the lapping carriage. The advantage of this slope is slightly to reduce the turn to be made in the storage carriage and to reduce accordingly the turn to be made in the lapping carriage. Given that the horizontal distance between the lapping carriage and the storage carriage varies in operation, the slope of the pinching zone is not constant. Typically it may be of the order of a few degrees.
Up to now it was normal to make the transportation path in the form of horizontal segments separated by turns at 180xc2x0. This was a disadvantage of the old machines, as described in EP-A-0 315 930, where the lapping carriage had at all times a speed double that of the storage carriage, so that each movement of the lapping carriage was precisely compensated for by a variation half as large of each of the two conveyor belt sections located on either side of the turn at 180xc2x0 formed on the storage carriage. In modern crosslappers, such a constant coupling between the two carriages is eliminated, and each of the carriages is driven by its own programmable servomotor, and thus programming of the storage carriage makes it possible in addition to compensate for the xe2x80x9cdefectxe2x80x9d caused by the not inconsiderable slope of the pinching zone.
To guide the web in the lapping carriage, it is proposed, in a non-limitative fashion according to the invention, that the outer surface of the outer conveyor belt should face obliquely downwards in the neck area formed with the outer surface of the internal conveyor belt. So, starting from the neck zone forming the lapping slot, the web may be deposited on one side or the other according to the direction of movement of the lapping carriage.
It is also advantageous in the lapping carriage, for the first angular area to be preceded by a preparatory zone where the web rests exposed on the internal conveyor belt located below, and, immediately upstream, by a zone where the web is covered by the external conveyor belt located above, in particular in the pinching zone, which external conveyor belt comes away from the web obliquely upwards in the preparatory zone. It has in fact been observed that at the exit of the pinching zone, the web was tending to stick to the upper conveyor belt and hence form a sort of wave above the conveyor belt located below. As a result of the layout that has just been described, the upper conveyor belt moves relatively abruptly apart from the web. This tends to reduce the effect of adherence and in addition the preparatory zone leaves time for the web to fall back on to the underlying conveyor belt before reaching the first angular area of the turn. This effect is improved even further as a result of the slight slope of the pinching zone that has been proposed above.
It is preferred according to the invention that the turning structure be applied to at least two turns in the crosslapper and in particular to a first turn in a storage carriage located at the entry to a pinching zone, then to a second turn located at the exit of the entirely rectilinear pinching zone in the lapping carriage. But the invention is also advantageous if only one turn is structured in accordance with the invention.
Other features and advantages of the invention will be apparent from the description below giving non-limitative examples.